var obj={
    birth:1990,
    getAge:function (year) {
        var b=this.birth;//返回：1990;
        var fn=(y)=>y-this.birth;//this.birth仍是1990
        return fn.call({birth:2000},year);
    }
};

console.log(obj.getAge(2015));//25

console.log(typeof 123);
// ```js
// 'use strict'
// var arr = [10, 20, 1, 2];
// arr.sort((x, y) => {
//     ???
// });
// console.log(arr); // [1, 2, 10, 20]
// ```

'use strict'
var arr = [10, 20, 1, 2];
arr.sort((x, y) => x-y);
console.log(arr); // [1, 2, 10, 20]
